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 Post subject: IT 465 carb problems...
PostPosted: Fri Oct 12, 2007 8:12 am 
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Joined: Mon Sep 03, 2007 4:11 pm
Posts: 21
Location: Westmont, NJ, USA
I am having trouble with my '82 IT 465. Bought it a while back and just now getting it running. Replaced head and base gaskets last week and rode it a little last weekend. It was very hard to start and once warmed up wanted to "run away". The engine would race at high RPM even after closing the throttle.

So yesterday I took the carb off and cleaned it out really well. Also lowered the float level a small amount as fuel dumped out the side vent tubes when the bike was leaning against anything, and it smokes a little and smelled rich. So put the carb back on and now it won't run at all. Fuel is dripping from the exhaust as I kick it over, and the plug is instantly wet-fouled. Tried lowering fuel level a few more times. Tried checking fuel level by turning on fuel, then off, then removing the bowl. Got the fuel level very low and it still pukes gas out the ehxuast. Not sure why it would do that even with the fuel level so low.

Any thoughts? What should the float height be? It's measured from the fuel bowl gasket surface on the carb body to the bottom of the float body itself, correct? Does that measurement stay accurate after the tabs (both inner acting on needle, and outer holding the floats) have been bent a few times and no longer exactly as originally placed? What should the fuel level be in the bowl (how high, or how full)? Can adyone advise? Was hoping to be able to ride this weekend. Thanks!


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PostPosted: Fri Oct 12, 2007 5:44 pm 
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Joined: Sat Jul 21, 2007 9:03 pm
Posts: 39
Location: Sparta, Wisconsin
The service data sheet I looked at for the '82 IT465J for the Mikuni VM38SS carb showed a float leve at 27mm +/- 1mm.

However, on another site, I saw the following listed as the stock settings for the VM38SS carb

Float level: 10.9-11.9 mm
Needle clip: 2nd groove
Jet needle: 6FJ40
Main jet: 320
Needle jet: R-0
Pilot jet: 50
Slide cutaway: 4.0

Maybe they are both measuring from different points. I don't know.

IT465 Service Data Sheet , from South Seattle Yamaha Sports Plaza parts page on 82 IT465.

The Mikuni VM Super Tuning Manual http://www.mikuni.com/pdf/vmmanual.pdf shows the float height at 22-24 mm and gives a diagram in Chapter 5 on how the measure it.

You may have different problems, but I've experienced the runaway effect before and eventually found it was a kinked throttle cable not allowing the slide to fully close.

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1976 CR 250M
1980 Yamaha DT100G
1980 XR 200
1981 CSR650


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PostPosted: Tue Oct 16, 2007 9:44 pm 
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Joined: Mon Sep 03, 2007 4:11 pm
Posts: 21
Location: Westmont, NJ, USA
Alright I think I got the float level pretty good on the bike. It runs much better and the throttle doesn't stick. It seems rather slow to rev down when you close the throttle, but I guess it's a heavier piston that what I'm used to riding.

The bike now starts relatively easy when cold. Within a couple kicks fires up. Rode alright up and down the street. Very hard to start when warm though. It'll backfire through the exhaust but doesn't want to start. It will eventually start though. Perhaps timing is retarded from where it should be? I'll have to mess with it some more tomorrow.


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PostPosted: Thu Oct 18, 2007 5:37 am 
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Joined: Mon Sep 03, 2007 4:11 pm
Posts: 21
Location: Westmont, NJ, USA
Timing was retarded as far as it would go. Set the timing and now it runs much better.


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PostPosted: Thu Oct 18, 2007 2:40 pm 
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Joined: Tue Aug 31, 2004 1:44 am
Posts: 283
Location: Maysville, AR
might check it over for air leaks.theres a very good chance it could need crankshaft seals.if the magneto side leaks it will cause it to lean out and cause a run away.you can tell when this happens with the throttle closed and the kill switch wont kill it.it will continue to sit there and scream.the only way to kill it is to shift the transmission into third or fourth gear and hold the front and rear brake hard then let the clutch out.let it out dont just dump the clutch out.that will usually get it shut down.you dont want to let it sit there and scream as the engine might seize or it might suffer catastrophic top end failure.might also have a badly worn top end and that will cause it to run too lean.

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PostPosted: Thu Nov 08, 2007 12:58 pm 
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Joined: Thu Jun 14, 2007 12:45 pm
Posts: 4
hi, me dt 175 did all that, problem was lose barrel new gasket set retorque barrel down .runs fine :)


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